resolv.conf question / timeout behaviour
Matus UHLAR - fantomas
uhlar at fantomas.sk
Wed Mar 31 12:55:58 UTC 2021
On 31.03.21 10:56, Tom Preissler via bind-users wrote:
>at my work place we have a three resolver setup in /etc/resolv.conf.
resolv.conf is not a BIND thing, it's configuration of system libraries.
>We had sometimes, though rarely, response times for DNS like 14000ms,
>due to the fact that the *first* listed resolver is down for maintenance
>reasons. The application we test this with is Oracle/TNSPing.
if this is an issue, you can run local caching DNS server like BIND or
dnsmasq. They can handle such timeouts better than most libraries.
>As a mitigation we therefore put in timeout:1, but we just recently got
>again a TNSPing response of 9000ms.
>I noticed in man resolv.conf this section on "timeout":
> Sets the amount of time the resolver will wait for
> a response from a remote name server before
> retrying the query via a different name server.
>| This may not be the total time taken by any
>| resolver API call and there is no guarantee that a
>| single resolver API call maps to a single timeout.
> Measured in seconds, the default is RES_TIMEOUT
> (currently 5, see <resolv.h>). The value for this
> option is silently capped to 30.
>I am intrigued by the above sentence marked with "|". Does anybody
>know what that means in detail, can anybody explain that please?
>I explained the reason for the 9000ms so that Oracle and its many processes
>all come together to resolve the DNS name and they *keep hitting* the first
>resolver - and "timeout" can't kick in due to parallel requests from different
>processes, hence the high overall response time.
Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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